In the WordPress core test suite the following assertion methods are available:

• $this->assertNotWPError()
• $this->assertWPError()

It would be great if this extension treated these methods as type-narrowing functions, so the following code would not throw an error in PHPStan:

$terms = wp_get_post_terms( $post_id, $taxonomy );
$this->assertNotWPError( $terms );
$this->assertCount( 0, $terms );

Currently this triggers the following error because $terms is assumed to be array|WP_Error on the last line.

[phpstan] Parameter #2 $haystack of method PHPUnit\Framework\Assert::assertCount() expects Countable|iterable, array|WP_Error given.